The present description relates generally to extremum seeking control strategies. The present description relates more particularly to regulating, via extremum seeking control, the amount of air that is flowing through a heating, ventilation and air conditioning (HVAC) system in order to reduce the amount of mechanical heating or cooling required within an air-handling unit (AHU).
Air-side economizers are used in AHUs to control the amount of air that is recirculated from within a building. The objective of economizer control logic is to control the mixing box dampers to achieve the right mixture of outside air and recirculated air in order to minimize the amount of energy consumed to heat or cool the building. Some AHU controllers use model-based control strategies that rely on a model of the system (e.g., a cooling coil model) as well as accurate measures of humidity and temperature for both the outdoor and return airstreams.
Extremum seeking control (ESC) is a class of self-optimizing control strategies that can dynamically search for the unknown and/or time-varying inputs of a system for optimizing a certain performance index. It can be considered a dynamic realization of gradient searching through the use of dither signals. The gradient of the system output with respect to the system input is typically obtained by slightly perturbing the system operation and applying a demodulation measure. Optimization of system performance can be obtained by driving the gradient towards zero by using an integrator in the closed-loop system. ESC is a non-model based control strategy, meaning that a model for the controlled system is not necessary for ESC to optimize the system. However, the algorithms used to implement an ESC strategy are often relatively complex.